The present invention relates to the use of ethylene homo- and copolymers stabilized by sterically hindered amines or their N-hydroxy or N-oxyl derivatives to produce articles of plastic and components for the storage and transport of vegetable oil esters.
The invention also relates to articles of plastic and components for the transport and storage of vegetable oil esters, which are produced using such stabilized polymers, and to ethylene homo- and copolymers stabilized by adding derivatives of quinoline or of diphenylamine.
In automotive fuel systems there is increasing use of plastic fuel tanks (PFTs) of polyethylene for spark-ignition and diesel-engined vehicles. For diesel-operated vehicles in particular the biodiesel fuels based on renewable raw materials are increasing in importance. The principal biodiesel fuels are based on vegetable oil methyl esters (VMEs), of which rapeseed oil methyl ester (RME) is the major representative. As the biodiesel fuels become more important, so will their storage and transport in containers or pipes made of polyethylene.
RME proves to be aggressive to many of the plastics used in the fuel system of a motor vehicle. Even high molecular mass polyethylene, as is used to produce PFTs and other hollow articles, may be attacked by RME, especially at elevated temperature. Its effect is to accelerate the embrittlement of the material, thereby impairing its long-term service properties.
Coating the interior of the hollow articles has been proposed for overcoming this problem. One disadvantage of an interior coating, however, is that it is highly complex to implement industrially and so always gives rise to considerable additional manufacturing costs. Moreover, in the PFT sector there is increasing use of co-extruded 6-layer tanks with a central barrier layer, whose additional internal fluorination would weigh heavily on the manufacturing costs of such PFTs.
It is an object of the present invention to provide ethylene homo- and copolymers, for producing articles of plastic and components for the storage and transport of vegetable oil esters, which are stabilized against the effect of vegetable oil esters.
We have found that this object is achieved by the use of ethylene homo- and copolymers stabilized by sterically hindered amines or by N-hydroxy or N-oxyl derivatives for producing articles of plastic and components for the storage and transport of vegetable oil esters.
We have also found articles of plastic and components for the transport and storage of vegetable oil esters, produced using such stabilized polymers, and ethylene homo- and copolymers stabilized by adding derivatives of quinoline or of diphenylamine.
Suitable stabilizers for the ethylene homo- and copolymers are N-hydroxy and N-oxyl derivatives of sterically hindered amines, but preferably the sterically hindered amines themselves.
By sterically hindered amines are meant all secondary amines whose substitution on the carbons adjacent to the amine nitrogen is such that no single hydrogen remains at these positions. Preference is given to derivatives of 2,2,6,6-tetramethylpiperidine, substituted either at the 4-position or on the amine nitrogen, and to derivatives of quinoline and of diphenylamine.
Examples of suitable amines are the following structures 
where the Rs are identical or different alkyls, cycloalkyls, aralkyls or aryls, alone or joined in pairs to form a ring system, and Y is a group required to complete a 5- or 6-membered ring. Examples of R are C1-C20-alkyl, especially C1-C8-alkyl, C5- or C6-cycloalkyl, benzyl or phenyl. Examples of Y are the alkylene groups xe2x80x94(CH2)2xe2x80x94 and xe2x80x94(CH2)3xe2x80x94.
Also suitable are the following structures 
where the aromatic rings may each carry 1 to 3 inert substituents such as C1-C4-alkyl, C1-C4-alkoxy or cyano, for example.
It is preferred to employ sterically hindered amine derivatives of cyclic amines, such as of piperidine or pyrrolidine compounds, whose ring may contain a further heteroatom such as nitrogen, oxygen or sulfur which is not adjacent to the hindered amine nitrogen. The steric hindrance is provided by substituents in both positions adjacent to the amine nitrogen, suitable substituents being hydrocarbon radicals which replace all 4 hydrogens of the xcex1-CH2-groups. Examples of substituents are phenyl, C3-C6-cycloalkyl, benzyl and especially C1-C6-alkyls, it being possible for alkyls attached to the same xcex1 carbon to be linked with one another in a 5- or 6-membered ring. The radicals set out individually under R1 and R2 are particularly preferred. Preference is given to using 2,2,6,6-tetraalkylpiperidine derivatives.
Preferred sterically hindered amines or their N-hydroxy or N-oxyl derivatives for use in accordance with the invention are those of the formula I 
where
R1 and R2 are C1-C4-alkyl or phenyl or together with the carbon to which they are attached are a 5- or 6-membered saturated hydrocarbon ring,
R3 is hydrogen, hydroxyl, amino or an m-valent, oxygen- or nitrogen-bonded organic radical or together with R4 is oxygen or a ring structure defined under R4,
R4 is hydrogen or C1-C12-alkyl or together with R3 is oxygen or together with R3 and the carbon to which they are attached is a ring structure 
where m is 1 when R3 and R4 unite to form a radical,
R5 is hydrogen, C1-C12-alkyl or xe2x80x94(CH2)zxe2x80x94COOR6,
R6 is identical or different C1-C18-alkyl,
X is hydrogen, hydroxyl or oxygen,
k is 0 or 1,
z and p are from 1 to 12 and
m is from 1 to 100.
R1 and R2 may, for example, be the C1-C4-alkyls methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl or tert-butyl or together may form tetra- or pentamethylene. R1 and R2 are preferably methyl.
Examples of R4 are hydrogen, the abovementioned C1-C4-alkyls and also pentyl, sec-pentyl, tert-pentyl, neopentyl, hexyl, 2-methylpentyl, heptyl, 2-methylhexyl, octyl, isooctyl, 2-ethylhexyl, nonyl, 2-methylnonyl, isononyl, 2-methyloctyl, decyl, isodecyl, 2-methylnonyl, undecyl, isoundecyl, dodecyl and isododecyl (isooctyl, isononyl and isodecyl are trivial names deriving from the carbonyl compounds obtained by oxo synthesis; cf. in this respect Ullmann""s Encyclopedia of Industrial Chemistry, 5th Edition, Vol. A1, pages 290-293, and Vol. A10, pages 284 and 285).
p is preferably 6-12, especially 9.
z is preferably 1-4, especially 2.
Examples of R5 in addition to hydrogen are the abovementioned C1-C12-alkyls. R5 is preferably hydrogen, C1-C4-alkyl or (CH2)zxe2x80x94COO(C1-C6-alkyl), and with particular preference is xe2x80x94CH2xe2x80x94CH2xe2x80x94COO(CH2)11xe2x80x94CH3 and xe2x80x94CH2xe2x80x94CH2xe2x80x94COO(CH2)13xe2x80x94CH3.
Possible examples of R6 are one of the abovementioned C1-C12-alkyls or tridecyl, isotridecyl, tetradecyl, pentadecyl, hexadecyl, heptadecyl or octadecyl. Dodecyl and hexadecyl are preferred.
Examples of preferred radicals R3 are the following m-valent radicals 
where
R7 is C1-C12-alkyl or xe2x80x94(CH2)zxe2x80x94COOR6 
R8 is hydrogen or C1-C18-alkyl,
R9 is C1-C18-alkyl, vinyl or isopropenyl,
R10 is C8-C22-alkyl,
R11 is hydrogen or an organic radical as is normally formed in the free-radical polymerization of the initial monomers,
k is 0 or 1,
x is from 1 to 12 and
n is an even number m.
If R3 is one of these radicals, then R4 is preferably hydrogen. The variable m can be from 1 to 100, and is preferably 1,2,3,4 or a number from 10 to 50, with mixtures generally being employed especially in the case of the oligomeric or polymeric radicals R3.
It has been found that oligomeric and polymeric amine derivatives where mxe2x89xa72 have a particularly good stabilizing action. Preference is also given to those amine derivatives comprising no hydrolyzable groups, such as ester groups.
Suitable radicals R7 are the same as for R5. R7 is preferably C1-C4-alkyl.
In addition to hydrogen, suitable radicals R8 are the same as for R6. R8 is preferably hydrogen.
Particularly suitable radicals R9 are vinyl, isopropenyl or C15-C17-alkyls.
Examples of suitable radicals R10 are the above-mentioned C8-C18-alkyls and also nonadecyl, icosyl, unicosyl and doicosyl. Preference is given here to mixtures of radicals R10 which differ in the length of their carbon chain.
The radicals R11 are hydrogen or organic radicals as formed in the free-radical polymerization of the initial monomers, in this case from an ethylene derivative and a maleimide derivative; in other words, for example, a radical formed from the polymerization initiator or from a free-radical intermediate, or another such radical, as the skilled worker is aware.
Other preferred amine compounds are:
2,2,6,6-tetramethylpiperidine,
2,2,6,6-tetramethylpiperidin-4-ol,
2,2,6,6-tetramethylpiperidin-4-one,
2,2,6,6-tetramethylpiperidin-4-yl acetate,
2,2,6,6-tetramethylpiperidin-4-yl 2-ethylhexanoate,
2,2,6,6-tetramethylpiperidin-4-yl stearate,
2,2,6,6-tetramethylpiperidin-4-yl benzoate,
2,2,6,6-tetramethylpiperidin-4-yl 4-tert-butylbenzoate,
Bis(2,2,6,6-tetramethylpiperidin-4-yl)succinate,
Bis(2,2,6,6-tetramethylpiperidin-4-yl)adipate,
Bis(2,2,6,6-tetramethylpiperidin-4-yl)sebacate,
Bis(2,2,6,6-tetramethylpiperidin-4-yl)n-butylmalonate,
Bis(2,2,6,6-tetramethylpiperidin-4-yl)phthalate,
Bis(2,2,6,6-tetramethylpiperidin-4-yl)isophthalate,
Bis(2,2,6,6-tetramethylpiperidin-4-yl)terephthalate,
Bis(2,2,6,6-tetramethylpiperidin-4-yl)hexahydroterephthalate,
N,Nxe2x80x2-bis(2,2,6,6-tetramethylpiperidin-4-yl)adipinamide,
N-(2,2,6,6-tetramethylpiperidin-4-yl)caprolactam,
N-(2,2,6,6-tetramethylpiperidin-4-yl)dodecylsuccinimide,
2,4,6-tris-[N-butyl-N-(2,2,6,6-tetramethylpiperidin-4-yl)]-s-triazine,
4,4xe2x80x2-ethylenebis(2,2,6,6-tetramethylpiperazin-3-one) and
tris(2,2,6,6-tetramethyl-1-oxylpiperidin-4-yl)phosphite
and the N-hydroxy and N-oxyl derivatives thereof.
Particularly preferred amine compounds are poly[3-icosyl(tetra-cosyl)-1-[2,2,6,6-tetramethylpiperidin-4-yl]pyrrolidine-2,5-dione] (Uvinul(copyright) 5050 H, from BASF AG, and especially poly[[6-(1,1,3,3-tetramethylbutyl)amino]-1,3,5-triazine-2,4-diyl][2,2,6,6-tetramethyl-4-piperidinyl)imino]-1,6-hexanediyl[(2,2,6,6-tetramethyl-4-piperidinyl)imino]] (Chimassorb(copyright)944, from Ciba Additives GmbH).
As with those of piperidine, preferred derivatives among those of quinoline and of diphenylamine are those oligomerized or polymerized through appropriate organic radicals. Examples which have proven suitable are polymerized 2,2,4-trimethyl-1,2-dihydroquinoline (TMQ), 6-ethoxy-2,2,4-trimethyl-1,2-dihydroquinoline (ETMQ), styrenized diphenylamine (SDPA) and octylated diphenylamine (ODPA). Such sterically hindered amines or their N-hydroxy or N-oxyl derivatives have to date been used principally for stabilizing rubber; ethylene homo- and copolymers stabilized by adding derivatives of quinoline or of diphenylamine were unknown prior to our invention.
The ethylene homo- and copolymers used in accordance with the invention comprise the sterically hindered amines or their N-hydroxy or N-oxyl derivatives preferably in an amount of from 100 to 5000 ppm, with particular preference in an amount of from 300 to 2000 ppm, based on the total mass of the polymers.
The polyethylene normally includes additional substances for thermal and in-process stabilization. These substances, which may also be used in combination with the RME resistance stabilizers used in accordance with the invention, include sterically hindered phenols, which may also contain nitrogen and/or sulfur as heteroelements, lactones, which may also contain nitrogen and/or sulfur as heteroelements, organic esters of phosphorous acid (e.g. trialkyl phosphites), which may also contain nitrogen and/or sulfur as heteroelements, and alkali metal and alkaline earth metal stearates. Examples of stabilizers from the class of sterically hindered phenols are benzenepropanoic acid 3,5-bis(1,1-dimethylethyl)-4-hydroxy-2,2-bis[[3-[3,5-bis(1,1-dimethylethyl)-4-hydroxyphenyl]-1-oxopropoxy]methyl]-1,3-propanediyl ester (Irganox(copyright)1010 from Ciba Additives GmbH), benzenepropanoic acid 3,5-bis(1,1-dimethylethyl)-4-hydroxyoctadecyl ester (Irganox(copyright)1076 from Ciba Additives GmbH), 4-[[4,6-bis(octylthio)-1,3,5-triazin-2-yl]amino]-2,6-bis(1,1-dimethylethyl)phenol (Irganox(copyright)565 from Ciba Additives GmbH), and N,Nxe2x80x2-hexamethylenebis(3,5-di-tert.butyl-4-hydroxyhydrocinnamamide) (Irganox(copyright)1098 from Ciba Additives GmbH). Examples of stabilizers from the class of the lactones are benzofuran-2-ones, such as 5,7-di-t-butyl-3-(3,4-dimethylphenyl)-3H-benzofuran-2-one. Examples of stabilizers from the class of the organic phosphites are 2,4-bis(1,1-dimethylethyl)phenol phosphite (Irganox(copyright)168 from Ciba Additives GmbH) and phosphorous acid {1,1xe2x80x2-biphenyl}-4,4xe2x80x2-diylbis-, -tetrakis[2,4-bis(1,1-dimethylethyl)phenyl] ester.
The incorporation of the stabilizers into the polymers can take place, for example, during the production of a granular base material or not until during the melting operation in preparation for shaping, which can take place, for example, by extrusion, injection molding or blow molding.
For use in the field of extrusion and blow molding the polyethylene preferably has a melt flow rate MFR (190/21.6) of from 1 to 25 g/10 min, in particular from 2 to 20 g/10 min, and for use in the field of injection molding an MFR (190/2.16) of preferably from 0.1 to 100 g/10 min, in particular from 0.2 to 10 g/10 min.
Particularly suitable for use in accordance with the invention are ethylene homo- and copolymers having a density of from 0.930 to 0.970, in particular from 0.940 to 0.960 g/cm3, and, with particular advantage, the polymer employed is HDPE as normally used, for example, to produce PFTs.
The ethylene homo- and copolymers used in accordance with the invention are outstandingly suited to the production of articles of plastic and components for the transport and storage of vegetable oil esters, especially vegetable oil methyl esters.
By articles of plastic and components in this context are meant all the plastics parts which are exposed to the vegetable oil esters for a prolonged period, especially plastic fuel tanks, but also parts such as pipes and feedlines, bottles, canisters, drums, etc.